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Fixing Device Capable Of Changing Smoothness Of Surface Of Toner Of Fixed Toner Image On Sheet And Image Forming Apparatus Using Said Fixing Device - Patent 6721532


1. Field of the InventionThe present invention relates to a fixing device for an image forming apparatus, and more particularly to the fixing device that provides desired image glossiness according to types of images.2. Discussion of the BackgroundIn an image forming apparatus, such as a copying machine, a facsimile machine, and a printer, a printed (copied) sheet is obtained by fixing an unfixed image onto a sheet as a recording material by heat and pressure in a fixing device.The fixing device may employ any one of fixing methods such as "heating roller fixing method", "radiant/flash fixing method", and "oven fixing method". Specifically, in the heating roller fixing method, a sheet carrying an unfixed image isconveyed while being sandwiched between a pair of rollers including a heating roller, and the unfixed image is fixed onto the sheet by heat of the heating roller. In the radiant/flash fixing method, a fixing device includes an infrared/Xenon lamp as aheat source, and an unfixed image is fixed onto a sheet by radiant heat. In the oven fixing method, heating elements are arranged in the vicinity of both sides of a sheet, and an unfixed image is fixed onto the sheet by convected heat.In the above-described fixing methods, the heating roller fixing method has been often employed because of advantages such as high thermal efficiency, high printing speed, high efficiency of heat transfer, and stabilized fixing efficiency. Further, a construction of an image forming apparatus including a fixing device using the heating roller fixing method may be simple, because the fixing device may also serve as a sheet conveying device.In the heating roller fixing method, when toner on a sheet is changed from a solid to liquid state by heat and pressure, the toner is changed from a partly fused and coalescent condition to a fluid and spread condition, and is finally in apenetrating condition on the sheet. As a result, particulate toner of an image, which has been likely to

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